An injection — administering medicine, a vaccine, etc., into the body with a syringe; the act or procedure of giving a shot.
インフルエンザの予防注射を受けた。
I received a flu vaccination (injection).
看護師が腕に注射をしたとき、少し痛みを感じた。
When the nurse gave the injection in my arm, I felt a little pain.
治療には週に一度の注射が必要だと言われた。
I was told the treatment requires a weekly injection.